In the related art, a supporting tool in a vertically installed heat treatment apparatus includes a pair of upper and lower end plates, for example, three holding members disposed vertically between the both end plates so as to extend therebetween, and is configured to hold a number of holding grooves formed in the longitudinal direction at regular intervals on these three holding members so as to open toward each other, so that a plurality of substrates are arranged horizontally with the centers thereof aligned with each other by being inserted between the holding grooves of the three holding members. However, in the supporting tool in such configuration, the entire weight of each substrate is supported only by the holding grooves at three points, and hence there is a problem such that when a thermal stress is applied abruptly to the substrates, crystal defect (slippage) or warp of the substrates may arise due to a tensile stress between the contact surfaces between the substrates and the holding grooves or a self-weight stress.
As a method of solving this problem, an invention described in Patent Document 1 is exemplified. In this description, the supporting tool includes a body portion and supporting portions which are provided on the body portion and comes into contact with the substrates. The surface of the supporting portion is formed of a silicon plate member having a surface area smaller than that of a flat surface of the substrate, and a thickness larger than that of the substrate (hereinafter, referred to as a plate structure supporting tool), so that the entire weight of the substrate is dispersed to alleviate the tensile stress and the self-weight stress, so that occurrence of slippage is restrained.
Patent Document 1, Pamphlet of International Publication No. WO2004/030073